The glycans (oligosaccharides and glycoconjugates) of human milk are powerful pathogen anti-adhesion compounds, and represent a novel class of antimicrobial agents. We propose to synthesize and test two of the most promising prototypes of fucosyl glycans (oligosaccharides and mucin) that naturally occur in human milk and have been shown, from in vitro, in vivo and molecular epidemiologic studies, to strongly inhibit NIAID Category B pathogens Campylobacter, Vibrio cholera, diarrheagenic Escherichia coli, and caliciviruses (noroviruses). These glycans function as receptor analogs that prevent infection by inhibiting pathogen binding to host cell surface glycans. Further, repeated pathogen exposure to such glycans does not result in resistance. Such glycans are stable for prolonged periods at room temperature, are intrinsically pleasant tasting, and could be produced and distributed economically as part of a drink or nutriment to individuals or populations at risk. A major roadblock to preclinical studies and human trials, however, has been the complexity and cost of synthesis of these fucosyl glycans. We propose to use recent breakthroughs in bioengineering for two generations of large-scale synthesis of fucosyl glycans in genetically modified microorganisms. Fucosyl oligosaccharides expressed in a bacterial construct will serve as standard synthetic monovalent inhibitors. A simultaneous but longer second generation of synthesis will be construction of a yeast that produces high molecular weight mucins whose polyvalent and multivalent expression of fucosylated moieties are expected to provide stronger and more broadly effective pathogen inhibition. The synthesis of these fucosyl glycans and their preclinical testing would be a quantum step towards a novel family of broadly effective therapeutics and prophylactics, would bring us to the threshold of human trials against Category B pathogens, and would represent a powerful new instrument for biodefense.